Homogeneous solid metallic anode for thin film microbattery

ABSTRACT

A battery, comprising a cathode comprising a cathode material in contact with a cathode current collector. The battery also comprises an electrolyte. The battery also comprises an anode comprising an electroplated homogeneous solid metallic alloy comprising 100 ppm to 1000 ppm Bi and 100 ppm to 1000 ppm In, and a remainder Zn.

BACKGROUND OF THE INVENTION

The present invention relates generally to the field of microsystemarchitectures and more particularly to a structure and composition of ananode in a thin film flexible microbattery.

A synergy of advances in materials science, microfabrication technology,biological micro-electro-mechanical systems (bioMEMS), microfluidics,and microelectronics has fueled a rapid growth of the capabilities andapplications of microsystems. For example, the advancing capabilities ofmicrosystems with an increasingly mature understanding of biologicalprocesses have a potential to significantly advance the quality ofhealthcare. Tiny tissue-integrated microsystems that enhance or monitorbiological functions (e.g., for diabetics) and can operate for months oryears at a time are envisioned. Such integrated devices must bebiocompatible, neurologically and cosmetically comfortable, andeffective—and with excellent reliability and longevity, especially ifsurgically implanted or if responsible for life-critical functions. Toachieve widespread application, they must be commercially viable andcost effective.

SUMMARY

Embodiments of the present invention disclose a battery, comprising acathode comprising a cathode material in contact with a cathode currentcollector. The battery also comprises an electrolyte. The battery alsocomprises an anode comprising an electroplated homogeneous solidmetallic alloy comprising 100 ppm to 1000 ppm Bi and 100 ppm to 1000 ppmIn, and a remainder Zn. Embodiments of the present invention alsodisclose a method for forming a battery. The method includes fabricatinga cathode in a first cavity in a first dielectric element. The methodfurther includes fabricating an anode in a second cavity in a seconddielectric element. The method further includes joining the cathode andthe anode in a complanate manner.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a diagram that shows two sides of a microsystem duringfabrication in accordance with an embodiment of the present invention.

FIG. 2 is a diagram that shows a top side of a microsystem that containsa portion of a microbattery in the microsystem during fabrication inaccordance with an embodiment of the present invention.

FIG. 3 is a diagram that shows a bottom side of a microsystem thatcontains a portion of a microbattery in the microsystem duringfabrication in accordance with an embodiment of the present invention.

FIG. 4 is a diagram that shows a positioning of a top side of amicrosystem that is free of its handler over a bottom side of themicrosystem that is still attached to its handler during fabrication inaccordance with an embodiment of the present invention.

FIG. 5 is a diagram that shows a positioning of a top side of amicrosystem that is free of its handler over a bottom side of themicrosystem that is free of its handler, before a rabbet joint is closedin accordance with an embodiment of the present invention.

FIG. 6 depicts the microsystem in FIG. 5 after the rabbet joint isclosed in accordance with an embodiment of the present invention.

FIG. 7 depicts a sectional view through the plane of FIG. 2 that shows acavity that is etched to accommodate cathode material during afabrication of the cathode side of a microbattery in accordance with anembodiment of the present invention.

FIG. 8 depicts a sectional view through the plane of FIG. 2 that shows alayer of a cathode-compatible current collector conductor over anadhesion metal layer in the cavity shown in FIG. 7 during a fabricationof the cathode side of the microbattery in accordance with an embodimentof the present invention.

FIG. 9 depicts a sectional view through the plane of FIG. 2 that shows alayer of photoresist deposited over the cathode-compatible currentcollector conductor in the cavity shown in FIG. 8 during a fabricationof the cathode side of the microbattery in accordance with an embodimentof the present invention.

FIG. 10 depicts a sectional view through the plane of FIG. 2 after apolymer bondable seal material is applied and patterned, exposing thecathode-compatible current collector conductor, the cathode currentcollector, during a fabrication of the cathode side of a microbattery inaccordance with an embodiment of the present invention.

FIG. 11 depicts a sectional view through the plane of FIG. 2 that showsa cathode material inserted over the cathode-compatible currentcollector conductor during a fabrication of the cathode side of themicrobattery in accordance with an embodiment of the present invention.

FIG. 12 depicts a sectional view through the plane of FIG. 3 that showsa cavity that is etched to accommodate anode material during afabrication of the anode side of a microbattery in accordance with anembodiment of the present invention.

FIG. 13 depicts a sectional view through the plane of FIG. 3 that showsa layer of seed metal deposited over an adhesion metal layer in thecavity shown in FIG. 12 during a fabrication of the anode side of themicrobattery in accordance with an embodiment of the present invention.

FIG. 14 depicts a sectional view through the plane of FIG. 3 that showsa layer of photoresist deposited over the seed metal in the cavity shownin FIG. 13 during a fabrication of the anode side of the microbattery inaccordance with an embodiment of the present invention.

FIG. 15 depicts a sectional view through the plane of FIG. 3 after aphotoresist material is applied and developed, exposing the seed metal,the anode current collector, during a fabrication of the anode side of amicrobattery in accordance with an embodiment of the present invention.

FIG. 16 depicts a sectional view through the plane of FIG. 3 after theseed metal is electroplated with a homogeneous solid composed of indium,bismuth, and zinc to form the anode, during a fabrication of the anodeside of a microbattery in accordance with an embodiment of the presentinvention.

FIG. 17 depicts a sectional view through the plane of FIG. 3 after alayer of photoresist is deposited over the seed metal and the anodeduring a fabrication of the anode side of a microbattery in accordancewith an embodiment of the present invention.

FIG. 18 depicts a sectional view through the plane of FIG. 3 after alayer of polymer bondable seal material is applied and patterned,exposing the surface of the anode during a fabrication of the anode sideof a microbattery in accordance with an embodiment of the presentinvention.

FIG. 19 depicts a sectional view through the plane of FIG. 3 after anelectrolyte separator material is deposited into the cavity in FIG. 18during a fabrication of the anode side of a microbattery in accordancewith an embodiment of the present invention.

FIG. 20 depicts a sectional view through the plane of FIG. 3 for theanode side and through the plane of FIG. 2 for the cathode side as thecathode side and the anode side are bonded together during a fabricationof the microbattery in accordance with an embodiment of the presentinvention.

FIG. 21 depicts a sectional view after the cathode side and the anodeside are bonded together to complete a fabrication of the microbatteryin accordance with an embodiment of the present invention.

FIG. 22 is a flowchart depicting fabrication steps of a cathode side ofa microbattery in accordance with an embodiment of the presentinvention.

FIG. 23 is a flowchart depicting fabrication steps of an anode side of amicrobattery in accordance with an embodiment of the present invention.

FIG. 24 is a flowchart depicting fabrication steps of a microsystemcontaining a microbattery in accordance with an embodiment of thepresent invention.

DETAILED DESCRIPTION

Detailed embodiments of the present invention are disclosed herein withreference to the accompanying drawings. It is to be understood that thedisclosed embodiments are merely illustrative of potential embodimentsof the present invention and may take various forms. In addition, eachof the examples given in connection with the various embodiments isintended to be illustrative, and not restrictive. Further, the Figuresare not necessarily to scale, some features may be exaggerated to showdetails of particular components. Therefore, specific structural andfunctional details disclosed herein are not to be interpreted aslimiting, but merely as a representative basis for teaching one skilledin the art to variously employ the present invention.

References in the specification to “one embodiment”, “an embodiment”,“an example embodiment”, etc., indicate that the embodiment describedmay include a particular feature, structure, or characteristic, butevery embodiment may not necessarily include the particular feature,structure, or characteristic. Moreover, such phrases are not necessarilyreferring to the same embodiment. Further, when a particular feature,structure, or characteristic is described in connection with anembodiment, it is submitted that it is within the knowledge of oneskilled in the art to affect such feature, structure, or characteristicin connection with other embodiments whether or not explicitlydescribed.

For purposes of the description hereinafter, the terms “upper”, “lower”,“right”, “left”, “vertical”, “horizontal”, “top”, “bottom”, andderivatives thereof shall relate to the disclosed present invention, asoriented in the drawing Figures. The terms “overlying”, “underlying”,“atop”, “on top”, “positioned on” or “positioned atop” mean that a firstelement, such as a first structure, is present on a second element, suchas a second structure, wherein intervening elements, such as aninterface structure may be present between the first element and thesecond element. The term “direct contact” means that a first element,such as a first structure, and a second element, such as a secondstructure, are connected without any intermediary conducting, insulatingor semiconductor layers at the interface of the two elements.

Contact lenses are potentially an excellent microsystem platform for amultitude of general diagnostic and vision-related functions. However,microsystems that are integrated into a contact lens or an ocularenvironment (e.g., a corneal implant) to perform ophthalmologicalfunctions have constraints in addition to those associated withintegration into other types of human tissue—a microsystem must haveextremely small dimensions, and be thin and flexible. The quest for suchmaterials that are both amenable to economic fabrication and have therequisite optical, electrical and biological properties are currently anactive area of research.

A microsystem that is suitable for integration into a contact lens,which includes an energy source and accommodates a variety of bioMEM andmicroelectronic mechanisms and that is realizable with economicmicrofabrication technologies is beneficial. A variety of health-relatedaugmentation, diagnostic, and monitoring functions could potentially behosted in such an ecosystem, greatly decreasing individual developmenttimes and costs.

A need for energy is a common requirement of active microsystems. Anenergy requirement may be minimal in many situations thus enabling amicrobattery to provide ample energy for a microsystem. For example, amicrobattery may be efficacious for a system embedded in a contact lens.However, batteries often contain substances that are toxic to humans,may be dimensionally awkward, and are opaque and inflexible, socompatible battery technologies are sought for ophthalmological devices.

In an embodiment of the present invention, a microsystem that can serveas a platform and ecosystem for a variety of microsystems and that canbe implanted into human tissue is presented. In an embodiment, themicrosystem is fabricated, using well-known processes, in two halves, atop side and a bottom side, that are joined after the two halves arefabricated. Each side is individually fabricated in a “C” shape, afterwhich the top side is aligned with and superimposed over the bottom sideand joined with the bottom side. An arc shaped gap in a resulting “C”shape that is comprised of the top side superimposed on the bottom side,is forced to close, forming an annulus.

In an embodiment, the microsystem includes one or more thin silicon die,interconnect wiring, and a battery energy source that is composed ofmaterials that are benign, thin, and flexible. One or more circuits andmemories are customized on the one or more silicon die to perform one ormore functions. The one or more circuits may be quantum, electrical,chemical, optical, mechanical, electromagnetic, microfluidic,biological, or a combination thereof. In an embodiment the microsystemcan be incorporated into a contact lens with a periphery of an annulusof the micro system aligning with a periphery of the contact lens andthe center of the annulus aligning with a center of the contact lens. Inanother embodiment, the microsystem is embedded in a corneal implant.

The present invention will now be described in detail with reference tothe Figures, in accordance with an embodiment of the present invention.

FIG. 1 depicts microsystem assembly 100 that, in an embodiment, consistsof two microassembly planars, microassembly top planar 101 andmicroassembly bottom planar 102. Microassembly top planar 101 includesmicrosystem top component 106 on temporary support wafer 103 andmicroassembly bottom planar 102 includes microsystem bottom component105 on temporary support wafer 104. In an embodiment microsystem topcomponent 106 and microsystem bottom component 105, are two sides of asingle microsystem that are joined to form a unified microsystem duringa fabrication process. Temporary support wafers 103 and 104 are removedafter the two sides are joined during a fabrication process.

In an embodiment, a side of a battery, a cathode side, is fabricated inmicrosystem top component 106 and the other side of the battery, ananode side, is fabricated in microsystem bottom component 105. Inanother embodiment, the anode side is fabricated in microsystem topcomponent 106 and the cathode side is fabricated in microsystem bottomcomponent 105. The cathode side of the battery and the anode side of thebattery are superimposed and joined when the two halves of the singlemicrosystem are joined.

FIG. 2 depicts microassembly top planar 101 in more detail. In anembodiment, a position of components on microassembly bottom planar 102is substantially similar to a position of components on microassemblytop planar 101. Those skilled in the art understand that a position ofcomponents on microassembly bottom planar 102 can be different from aposition of components on microassembly top planar 101.

In an embodiment, top polymer flex substrate 201 is a flex polymermaterial, e.g., polyethylene, or Kapton® (Kapton® is a registeredtrademark of DuPont Corporation), that is deposited on temporary supportwafer 103 to provide a support matrix material for a creation of one ormore structures in microsystem top component 106. Cavity 212 is etchedinto top polymer flex substrate 201 to accommodate a possibleprotuberance caused by one or more dies and pads on microsystem bottomcomponent 105 to enable microsystem top component 106 to be joined withmicrosystem bottom component 105 in a complanate manner. The termcomplanate is defined as “made level” and as “put into or on one plane”.

Cavity 203 is etched into polymer flex substrate 201 to accommodatebattery material 204 and polymer bondable seal material 202. In anembodiment, an etching of cavity 203 is accomplished by masking aphotoresist in combination with reactive-ion etching (RIE). RIE is anetching technology that uses chemically reactive plasma to removematerial deposited on wafers. In other embodiments the etching isaccomplished by using a metal mask and a laser. Those skilled in the artunderstand there are many ways to etch cavity 203 and that polymerbondable seal material 202 is a photopatterned polymer bondable sealmaterial that is photo-definable.

In an embodiment, rabbet joint adhesive 208 adheres to a substantiallysimilar rabbet joint adhesive on microsystem bottom component 105(rabbet joint adhesive 308 in FIG. 3) to bond the ends of a microsystemin a “C” or arc shape together into a shape of a closed annulus. In anembodiment, rabbet joint adhesive 208 and 308 are polymer adhesives thatbond when placed in contact with each other and cured using pressure, orheat, or UV, or a combination thereof. In an embodiment, rabbet jointadhesive 208 and 308 are electrically conductive to form an electricalas well as a mechanical connection. A rabbet joint is a common carpentryjoint in which a recess is formed on a first item and on a second itemto be joined by the rabbet joint, such that a recess on a first itemfits into a protuberance on a second item and a protuberance on thefirst item fits into a recess on the second item.

Silicon die 206 is a processing and/or memory element that is operableon quantum, electrical, chemical, optical, mechanical, microfluidic,electromagnetic, or biological principles and phenomena, or acombination thereof that provides a customizable functionality to anassembled microsystem. In an embodiment, one or more silicon diessubstantially similar to silicon die 206 are attached to top polymerflex substrate 201. In an embodiment, silicon die 206 is between 20 μmand 100 μm in thickness.

Polymer bondable seal material 213 seals a portion of a surface ofmicrosystem top component 106. Those skilled in the art understand thatpolymer bondable seal material 213 is a photopatterned polymer bondableseal material. Wiring trace 210 is an electrical conductor from batterymaterial 204 to silicon die 206. Pads 209 are electrical contacts thatprovide electrical connections to silicon die 206 via wiring trace 214.In an embodiment, wiring trace 210 and wiring trace 214 are comprised ofindium tin oxide (ITO) on a blend of titanium and tungsten (TiW). In anembodiment, hole 207 provides a path for one or more connective wiresfrom pads 209 to one or more mechanisms that are external to microsystemtop component 106. Conductive adhesive 211 adheres to a substantiallysimilar conductive adhesive on microsystem bottom component 105 to bondmicrosystem top component 106 with microsystem bottom component 105.Conductive adhesive 211 is an electrical conductor and, in anembodiment, provides for an electrical connection between microsystemtop component 106 and microsystem bottom component 105. In anembodiment, the electrical connection enables one or more batteries in amicrosystem to be connected in series or parallel and/or enables signalsto propagate between two or more locations in the microsystem.

In an embodiment, plane 205 depicts a cross-sectional view of a cathodeside of a microbattery, the fabrication of which is discussed inreference to FIGS. 7 through 11 and FIGS. 20 and 21.

FIG. 3 depicts microassembly bottom planar 102 in more detail. In anembodiment, a position of components on microassembly bottom planar 102is substantially similar to a position of components on microassemblytop planar 101. Those skilled in the art understand that a position ofcomponents on microassembly bottom planar 102 can be substantiallydifferent from a position of components on microassembly top planar 101.

In an embodiment, bottom polymer flex substrate 301 is a flex polymermaterial, e.g., Kapton® or polyethylene, which is deposited on temporarysupport wafer 104 to provide structural support for microsystem bottomcomponent 105. Cavity 312 is etched into bottom polymer flex substrate301 to accommodate a protuberance caused by silicon die 206 and pads 209on microsystem top component 106 so that microsystem top component 106can be joined with microsystem bottom component 105 in a complanatemanner.

Cavity 303 is etched into bottom polymer flex substrate 301 toaccommodate battery material 304 and polymer bondable seal material 302.In an embodiment, an etching of cavity 303 can be accomplished withphotoresist in combination with reactive-ion etching. In otherembodiments, the etching is accomplished with a metal mask and a laser.Those skilled in the art understand that there are many ways to etchcavity 303 and that polymer bondable seal material 302 is aphotopatterned polymer bondable seal material that is photo-definable.In an embodiment, rabbet joint adhesive 308 adheres to rabbet jointadhesive 208 on microsystem top component 106 to bond the ends of amicrosystem in a “C” or arc shape together into a shape of a closedannulus.

Silicon die 306 is a processing and/or memory element that is operableon quantum, electrical, chemical, optical, mechanical, microfluidic,electromagnetic, or biological principles and phenomena, or acombination thereof that provides a customizable functionality to anassembled microsystem. In an embodiment, one or more silicon diessubstantially similar to silicon die 306 are attached to bottom polymerflex substrate 301. In an embodiment, silicon die 306 is between 20 μmand 100 μm in thickness.

Polymer bondable seal material 313 seals a portion of a surface ofmicrosystem bottom component 105. Those skilled in the art understandthat polymer bondable seal material 313 is a photopatterned polymerbondable seal material that is photo-definable. Wiring trace 310 is anelectrical conductor from battery material 304 to silicon die 306. Inother embodiments, a plurality of wiring traces distributes energy toenergy consuming components such as silicon die 306. Pads 309 areelectrical contacts that provide electrical connections to silicon die306 via wiring trace 314. In an embodiment, wiring trace 310 and wiringtrace 314 are comprised of indium tin oxide (ITO) on a blend of titaniumand tungsten (TiW). In an embodiment, hole 307 provides a path for oneor more connective wires from pads 309 to one or more mechanisms thatare external to microsystem bottom component 105. Conductive adhesive311 adheres to conductive adhesive 211 on microsystem top component 106to bond microsystem top component 106 with microsystem bottom component105. Conductive adhesive 311 is an electrical conductor and in anembodiment, provides for an electrical connection between microsystemtop component 106 and microsystem bottom component 105. In anembodiment, the electrical connection enables one or more batteries in amicrosystem to be connected in series or parallel and enables signals topropagate between two or more locations in a microsystem.

In an embodiment, plane 305 depicts a cross-sectional view of a cathodeside of a microbattery, the fabrication of which is discussed inreference to FIGS. 12 through 21.

FIG. 4 depicts microsystem top component 106, with temporary supportwafer 103 removed, aligned and bonded with microsystem bottom component105 on microassembly bottom planar 102 with conductive adhesive 211adhering to conductive adhesive 311.

FIG. 5 depicts microsystem top component 106, aligned and bonded withmicrosystem bottom component 105 with temporary support wafer 104removed. Rabbet joint adhesive 308 on microsystem bottom component 105is in a position to bond with rabbet joint adhesive 208 on microsystemtop component 106 when the ends of “C” shaped microsystem 500 are joinedand bonded together. In an embodiment, rabbet joint adhesive 208 and 308are electrically conductive to form an electrical as well as amechanical contact.

FIG. 6 depicts microsystem 600 that is “C” shaped microsystem 500 aftera gap in the “C” shaped microsystem 500 is closed by a bonding of rabbetjoint adhesive 308 on microsystem bottom component 105 with rabbet jointadhesive 208 on microsystem top component 106. A closing of the gap in“C” shaped microsystem 500 compresses a material on an inside of the “C”and stretches a material on an outside of the “C”, causing the materialon the inside to buckle upward relative to material on an outside of the“C”, resulting in a conical shape to an upper surface of an annulus. Inan embodiment, a curvature of the upper surface of the annulus conformsgenerally to a curvature of a convex outer surface of a concavo-convexshaped contact lens, enabling microsystem 600 to be efficaciouslyembedded in the contact lens. If embedded in a contact lens, microsystem600 capacitates vision through a central circular “donut” hole in theconical shaped annulus that is a shape of microsystem 600. Theflexibility of microsystem 600 enables it to be transformed from theplanar shape of microsystem 500 into the conical shape of microsystem600 by squeezing the gap in “C” shaped microsystem 500 together. Thisshape transformation could not be accomplished if microsystem 500 wasrigid with little or no flexibility. The flexibility of microsystem 500is defined by a radius of curvature of between about 4 mm and about 20mm.

Embodiments of the present invention recognize that microsystem 600 iscapable of being incorporated into a contact lens. If microsystem 600 isincorporated into a contact lens, its shape and dimensions are definedby the shape of the human eye. The inner radius of the cone shapeachieved after closing the gap in “C” shaped microsystem 500 isconstrained by the need to have a sufficient visual opening. A minimumradius of about 3 mm for the inner radius is practical, and a largerradius is desirable. The outer radius of the cone shape is limited bythe size of the cornea and the contact lens material around the coneshape of microsystem 600. The outer radius is less than about 9 mm.

The cone slope (as measured from the central axis of the cone) is afunction of the inner and outer radii and is fabricated so that the coneslope approximates the slope of the eye surface between the inner andouter radius, within a range that is bounded by the contact lensthickness. Desired cone surface angles depend the range of eyedimensions that are envisioned as application targets for microsystem600. If a corneal radius of curvature is R (about 8 mm), then for aninner cone radius of ri and outer cone radius of ro, a reasonable mediancone angle A, is determined using Formula (1).

$\begin{matrix}{A = {\arctan \left\{ \frac{\sqrt{R^{2} - {ri}^{2}} - \sqrt{R^{2} - {ro}^{2}}}{{ro} - {ri}} \right\}}} & {{Formula}\mspace{14mu} (1)}\end{matrix}$

This is the angle between a surface of a cone and a central axis of thecone. The central axis of the cone is also collinear with the radius ofa sphere (e.g., an eye) that the cone penetrates with the apex of thecone at the center of the sphere. The cone angle can be adjusted fromcone angle A if the contact lens is not spherical. Typical cone anglesare likely to be between about 15 and about 40 degrees. A cone thusdescribed can be cut and flattened into a flat arc of inner radiusri/cos A, outer radius ro/cos A, and with an arc angle, cos A*360degrees.

In an embodiment, microsystem 600 incorporates a microbattery to provideenergy for one or more functions realized in microsystem 600. In anembodiment, a cathode of a microbattery is fabricated on microsystem topcomponent 106 and an anode of the microbattery is fabricated onmicrosystem bottom component 105. The completed microbattery is formedwhen the cathode is placed in contact with the anode during afabrication process.

In an embodiment, microsystem 600 comprises one or more of thefollowing: one or more thermal, pressure, chemical, and biochemicalsensors; one or more medicine delivery mechanisms for release and/orcontrolled release of liquids and/or bioactive chemicals, one or morelight based sensors, indicators and/or displays; one or more radiofrequency, visible light, infrared, and audio transmitters and/orreceivers. In an embodiment, microsystem 600 comprises one or moretactile indicators, vibrators, photonic, particle, image, and/or tactilesensors. In an embodiment, microsystem 600 is embedded in a contact lensor is a corneal implant wherein microsystem 600 enhances and/or enablesvision. In an embodiment, microsystem 600 is embedded in a contact lensand adjusts a focal length of the contact lens using an electro-opticalmechanism on microsystem 600 or controlled by microsystem 600. Examplesof an electro-optical mechanism are described in U.S. patent applicationSer. No. 14/340,164 filed concurrently with this application entitled“Variable Focal Length Lens,” published on Jan. 29, 2015 as U.S.Publication No. 2015-0029424A1, the entirety of which is incorporated byreference herein. In an embodiment, microsystem 600 comprises a heatingelement. In an embodiment, microsystem 600 comprises a microfluidic ormicromechanical mechanism such as a gyroscope or motion sensor. In anembodiment, microsystem 600 comprises a scene, and/or facial, and/ormovement (e.g., gate) recognition mechanism. In an embodiment,microsystem 600 is embedded in each of two contact lenses, one contactlens in each of two eyes, and a microsystem 600 in a contact lens in aneye communicates with another microsystem 600 that is in another contactlens that is in another eye of a same person or in an eye of anotherperson.

FIGS. 7-11 depict a cathode side of the microbattery, transected byplane 205 of FIG. 2, at different steps during a fabrication process, inaccordance with an embodiment of the present invention. FIG. 7 showscavity 203 etched into top polymer flex substrate 201 that is depositedon temporary support wafer 103 to accommodate cathode material in thefirst step. In an embodiment, temporary support wafer 103 is made ofglass.

FIG. 8 shows a next step in which an adhesion metal layer 801 and alayer of transparent conducting oxide 802 are deposited as a layer incavity 203 creating layered cavity 803 and over a surface of top polymerflex substrate 201. In an embodiment, adhesion metal layer 801 istitanium tungsten (TiW), however, those skilled in the art understandthat titanium (Ti) or tantalum (Ta) or other suitable material can beused in place of TiW. In an embodiment, adhesion metal layer 801 servesas a metal barrier to prevent electrolyte egress from the cathode of thebattery. In an embodiment, adhesion metal layer 801 serves as anelectrical contact to the battery. In an embodiment, adhesion metallayer 801 has discontinuities to electrically isolate a mechanical sealbonded to adhesion metal layer 801 from a battery electrical circuit.

In an embodiment, transparent conducting oxide 802 is indium tin oxide(ITO), however, those skilled in the art understand that othertransparent conducting oxides can be used, such as indium zinc oxide(IZO), Al-doped zinc oxide (AZO), or Ga-doped zinc oxide (GZO).Transparent conducting oxide 802 serves as a cathode current collector.In an embodiment, a combination of ITO, IZO, AZO, and GZO can be used.In an embodiment, transparent conducting oxide 802 can be replaced withtitanium (Ti), gold (Au), carbon-coated Ti or carbon-coated Au. In anembodiment, transparent conducting oxide 802 can be thin, with athickness of between 20 nm and 200 nm, which provides for a mechanicallyflexible battery and consumes less space than a material requiring athicker layer for the cathode current collector. A mechanically flexiblebattery facilitates a use of the battery in a system that can conform toa biological shape in a living tissue, for example. In an embodiment,the battery has a flexibility defined by a radius of curvature ofbetween about 4 mm and 20 mm.

FIG. 9 shows a next step in a fabrication of the cathode in which alayer of photoresist 901 is deposited over transparent conducting oxide802, completely fills layered cavity 803 and forms a layer ofphotoresist 901 over top polymer flex substrate 201. A patterning ofphotoresist 901 defines wiring trace 210 and wiring trace 214 and apattern of transparent conducting oxide 802 and adhesion metal layer801. In a subtractive etching process, unmasked areas of transparentconducting oxide 802 and adhesion metal layer 801 are removed. In otherembodiments, a plurality of wiring traces are defined to meet arequirement of microsystem 600.

FIG. 10 shows a next step in a fabrication of the cathode in whichphotoresist 901 is completely stripped and polymer bondable sealmaterial 1001 is applied and patterned, creating cavity 1002 andexposing a surface of transparent conducting oxide 802, which is thecathode current collector. Polymer bondable seal material 1001 that isleft after etching to create cavity 1002 is permanent and is notstripped. Polymer bondable seal material 1001 is polymer bondable sealmaterial 202, of FIG. 2, viewed from a different perspective.

FIG. 11 shows a step in a fabrication of the cathode side of the batteryin which cathode material 1101 is inserted into cavity 1002 formingcathode side 1102 of the battery. In an embodiment, cathode material1101 is manganese dioxide (MnO2), however, those skilled in the artunderstand that other suitable materials can be used. Cathode material1101 can be electroplated nickel hydroxide (NiOOH) or a mixture of MnO2with or without binder. Because transparent conducting oxide 802 isthin, less space is consumed by transparent conducting oxide 802,leaving more space for cathode material 1101, enabling a construction ofa battery that contains more energy relative to a battery of a same sizethat uses a thicker material for a cathode current collector. In anembodiment, cathode material 1101 is in direct contact with transparentconducting oxide 802, a current collector.

Having described embodiments of a cathode (which are intended to beillustrative and not limiting), it is noted that modifications andvariations may be made by persons skilled in the art in light of theabove teachings. It is therefore to be understood that changes may bemade in the particular embodiments disclosed which are within the scopeof the present invention as outlined by the appended claims.

FIGS. 12-19 depicts an anode side of the microbattery transected byplane 305 of FIG. 3 at different steps during a fabrication process, inaccordance with an embodiment of the present invention. FIG. 12 showscavity 303 etched into bottom polymer flex substrate 301 that isdeposited on temporary support wafer 104 to accommodate anode materialin the first step. In an embodiment, temporary support wafer 104 is madeof glass.

FIG. 13 shows a next step in which an adhesion metal layer 1301 and alayer of seed metal 1302 are deposited as a layer in cavity 303 creatinglayered cavity 1303 and over a surface of bottom polymer flex substrate301. In an embodiment, adhesion metal layer 1301 is titanium tungsten(TiW), however, those skilled in the art understand that titanium (Ti)or tantalum (Ta) or other suitable material can be used in place of TiW.In an embodiment, adhesion metal layer 1301 serves as a metal barrier toprevent electrolyte egress from the anode of the battery. In anembodiment seed metal 1302 is copper (Cu), however, those skilled in theart understand that seed metal 1302 may be another appropriate materialsuch as gold (Au). Seed metal 1302 serves as an anode current collector.In an embodiment, adhesion metal layer 1301 serves as an electricalcontact to the battery. In an embodiment, adhesion metal layer 1301 hasdiscontinuities to electrically isolate a mechanical seal bonded toadhesion metal layer 1301 from a battery electrical circuit.

FIG. 14 shows a next step in a fabrication of the anode in which a layerof photoresist 1401 is deposited over seed metal 1302, completely fillslayered cavity 1303 and forms a layer of photoresist 1401 over bottompolymer flex substrate 301.

FIG. 15 shows a next step in a fabrication of the anode in whichphotoresist 1401 is photopatterned into a shape exposing a surface ofseed metal 1302 at the bottom of cavity 1502. Seed metal 1302 is theanode current collector.

FIG. 16 shows a next step in a fabrication of the anode in which theexposed surface of seed metal 1302 is electroplated with a homogeneoussolid composed of indium, bismuth, and zinc (In/Bi/Zn) to form anodematerial 1601. In an embodiment, anode material 1601 is a homogeneoussolid metallic alloy composed of 100 ppm to 1000 ppm Bi, 100 ppm to 1000ppm In, and the remainder is Zn, however, those skilled in the artunderstand that anode can be composed of another material, such as zincmetal. An analytical technique such as Proton Induced X-ray Emission(PIXE) can be used to empirically determine the amount of Bi, In, and Znused in the anode. In an embodiment, anode material 1601 is 1 μm to 50μm thick, however, those skilled in the art understand that anodematerial 1601 can be another appropriate thickness. The remainder ofphotoresist 1401 is removed after anode material 1601 is electroplatedon the exposed surface of seed metal 1302.

In an embodiment of the present invention, anode material 1601 iselectroplated in a bath in an electroplating tank that contains In in aconcentration in a range of 100 ppm to 1000 ppm, Bi in a concentrationin a range of 100 ppm to 1000 ppm, with In in a nominal concentration of300 ppm+/−200 ppm and Bi in a nominal concentration of 300 ppm+/−200ppm, and Zn. In an embodiment of the present invention, theelectroplating tank has sufficient convection to keep the electroplatedcomposition of anode material 1601 uniform independent of its thicknessand/or the current used in the electroplating process. The current usedelectroplating process is pulsed to keep the electroplated compositionof anode material 1601 uniform independent of its thickness.

In another embodiment, the component elements of anode material 1601 areelectroplated on the exposed surface of seed metal 1302 in separatelayers, one component element per layer, in separate electroplatingsteps and then the separate layers are annealed to create a singlehomogeneous layer.

FIG. 17 shows a next step in a fabrication of the anode in which a layerof photoresist 1701 is deposited over seed metal 1302 and anode material1601 protecting anode material 1601. A patterning of photoresist 1701defines wiring trace 310 and wiring trace 314 and a pattern of seedmetal 1302 and adhesion metal layer 1301. In a subtractive etchingprocess, unmasked areas of seed metal 1302 and adhesion metal layer 1301are removed. In other embodiments, a plurality of wiring traces aredefined to meet a requirement of microsystem 600.

FIG. 18 shows a next step in a fabrication of the anode in whichphotoresist 1701 is completely stripped and polymer bondable sealmaterial 1801 is applied and patterned, creating cavity 1802 andexposing a surface of anode material 1601. Polymer bondable sealmaterial 1801 that is left after creating cavity 1802 is permanent andis not stripped. Polymer bondable seal material 1801 is polymer bondableseal material 302 of FIG. 3 viewed from a different perspective.

FIG. 19 shows a next step in a fabrication of the anode in whichelectrolyte separator material 1901 is deposited into cavity 1802forming anode side 1902 of the microbattery. In an embodiment,electrolyte separator material 1901 is soaked in an electrolyte, in awet assembly. In an embodiment, the electrolyte has a pH in a range of 3to 7. In an embodiment, the electrolyte is one or more of: ammoniumchloride, an aqueous salt solution such as KOH, zinc chloride, or zincacetate with an additive such as ZnO. In an embodiment, electrolyteseparator material 1901 is treated to render electrolyte separatormaterial 1901 hydrophylic so that electrolyte separator material 1901can be filled with electrolyte through a fill port, in a dry assembly.In an embodiment, electrolyte separator 1901 comprises one or more of aflexible porous material, a gel, a sheet that is from 10 μm to 100 μm inthickness that is composed of cellulose, cellophane, polyvinyl acetate(PVA), PVA/cellulous blends, polyethylene (PE), polypropylene (PP), or amixture of PE and PP.

Having described embodiments of an anode that is an electroplatedhomogeneous solid metallic alloy (which are intended to be illustrativeand not limiting), it is noted that modifications and variations may bemade by persons skilled in the art in light of the above teachings. Itis therefore to be understood that changes may be made in the particularembodiments disclosed which are within the scope of the presentinvention as outlined by the appended claims.

Embodiments of the present invention recognize that, in a thin-filmmicrobattery, an electroplated anode has many advantages over an anodecomposed of a mixture of particles that may be in the form of a paste,for example. The smallest dimension of a structure composed of a mixtureof particles is limited to the size of the largest particle in themixture. For example, if the diameter of the largest particle is about25 microns, a typical size of a particle in a metallic powder, a minimumanode thickness of about 25 microns is potentially possible with amaterial that incorporates the particle, if constraints imposed by afabrication process are not taken into account.

Embodiments of the present invention can achieve a thickness of 1 micronfor anode material 1601, an electroplated homogeneous solid metallicalloy. Therefore the minimum patternable line width of the electroplatedhomogeneous solid metallic alloy is 1 micron or less, which facilitatesits use in microbatteries and micro-miniaturized devices. Embodiments ofthe present invention recognize that common fabrication techniques(e.g., screening, stenciling, and printing) employed to form a structureusing particle-based material incorporating particles 25 microns insize, limit a minimum dimension of the material to something greaterthan 100 microns.

In addition to being patternable down to a 1 micron dimension, theelectroplated homogeneous solid metallic alloy has essentially noporosity, increasing its density and efficiency as it contains no wastedspace. In one embodiment, the percentage of voids by volume in theelectroplated homogeneous solid metallic alloy is less than 0.01%,preferably 0%. It is denser than a particle-based material that oftencontains voids, conductivity-enhancing additives, and binder additivesthat envelope the particles to hold them in place in a battery. Becauseof its density, the electroplated homogeneous solid metallic alloy canbe plated to an essentially mirror smooth surface, whereas thesmoothness of a particle-based material is defined by the sizes of theparticles that it contains. In one embodiment, the proportions of theconstituent components in anode material 1601 are homogeneous to thedegree that the proportion of any constituent component (In, Bi, Zn)within a volume defined within the anode material, such as film heightof anode material (in mm) cubed, deviates by less than 10% from the bulkproportion of that constituent component in the total volume of theanode material.

Embodiments of the present invention recognize that anode material 1601is more volume-efficient than a particle-based material as the entiretyof its mass participates in its function whereas only a portion of thetotal mass of the material composed of a mixture of particlesparticipates in its function. Therefore a material with low or noporosity is advantageous in a microbattery. The size of a microbatteryis a significant factor in determining whether a use of the battery ispractical in an application or in a given physical environment.

In an embodiment, anode material 1601 is a homogeneous solid metallicalloy composed of 100 ppm to 1000 ppm Bi, 100 ppm to 1000 ppm In, andthe remainder is Zn and because it is a continuous film, its resistivityis close to that of bulk zinc which is about 5×10⁻⁸ to 6×10⁻⁸ ohm-m. Theresistivity of a zinc paste composed of particles is about 10000×10⁻⁸ohm-m, which is about a 2000 fold increase in resistivity over that ofanode material 1601. Embodiments of the present invention recognize thatan anode material with a low resistivity is advantageous in amicrobattery because the resistivity of the anode material contributesto the internal resistance of the microbattery. The greater a battery'sinternal resistance is, the slower the battery is in providing pulses ofcurrent to a load, i.e., the rise time of a current pulse increases asthe internal resistance increases. Therefore for a microbattery that isrequired to provide significant pulses of current, a continuous filmanode material is better than a porous paste approach that uses aparticle-based material. In an embodiment, the surface the exposedsurface of seed metal 1302 is textured so that electroplated anodematerial 1601 is textured to increase its surface area to enhance itsability to provide large current draws.

In addition, the homogeneous solid metallic alloy of anode material 1601is mechanically stronger than that of a particle-based paste. Thestrength of anode material 1601 is about 100 MPa while that of aparticle-based paste is at least 1000 times lower. The strength of ananode material contributes to the physical robustness of a microbattery.Because anode material 1601 is electroplated to seed metal 1302, theinterface between seed metal 1302 and anode material is exceptionallystrong, while the anode/current collector interface of a particle-basedpaste anode material is relatively weak and contact between the anodeand the current collector is predominately maintained only by forcesexternal to the interface. In a flexible microbattery, the interfacebetween anode material 1601 and seed metal 1302 is unlikely to crack ordelaminate under flexing while that of a particle-based anode materialis much more apt to crack or delaminate under flexing.

The homogeneous solid metallic alloy of anode material 1601 mayinterface with a variety of electrolytes (e.g., alkaline (KOH), zincacetate, zinc chloride, and ammonium chloride) without a need toreformulate a mixture of the components of anode material 1601. Becausea particle-base paste requires a binder to hold its constituentparticles together, the characteristics of a chemical reaction at thebinder/electrolyte contact interface must be carefully considered whenselecting appropriate materials, as only specific binders can work witha specific electrolyte and vise versa, making the design and developmentof such a structure relatively involved compared to that of homogeneoussolid metallic alloy of anode material 1601.

Another consideration in a development of a particle-based paste anodeis that of an optimization of the relative quantities of the binder,conductivity enhancers, and the constituent particles is the paste, andoptimizing the solvent that is used during screening, stenciling, orprinting of the paste. Tradeoffs must be made between resistivity andmechanical properties of the paste, and flow enhancers that fabricationtechniques may require during construction of particle-based pasteanode. Anode material 1601 is optimized in situ so no optimization ortradeoffs are required during its development, and since it is not apaste, no solvent is necessary to enhance its handling characteristicsduring fabrication.

FIG. 20 shows a next step in a fabrication of the microbattery in whichcathode side 1102 is bonded with anode side 1902 to from a battery.Temporary support wafers 103 and 104 are a part of microbatteryfabrication structure 2001 and are removed in a next step in afabrication of the microbattery. In an embodiment, the anode side andthe cathode side of the microbattery are fabricated in parallel. FIG. 1also depicts a joining of microassembly top planar 101 withmicroassembly bottom planar 102 such that the two sides of themicrobattery would be joined together. In an embodiment, the two sidesof the microbattery are hermetically joined and sealed together.

FIG. 21 shows completed microbattery 2102 after temporary support wafers103 and 104 are removed from battery fabrication structure 2001.Electrolyte separator material 1901 is in direct contact with cathodematerial 1101. In an embodiment temporary support wafers 103 and 104 areremoved via one or more laser cuts.

In an embodiment, a thickness of microbattery 2102 is no greater thanabout 150 μm. In an embodiment, microbattery 2102 has a volume less than1 cubic mm. In an embodiment, microbattery 2102 has a flexibilitydefined by a radius of curvature of between about 4 mm and 20 mm. In anembodiment, microbattery 2102 has metal or dielectric coating applied toan exterior plane and/or an end surface of one or more of a surface orsubstrate and/or adhesive join on microbattery 2102 to create a sealinglayer to prevent electrolyte egress. In an embodiment, microbattery 2102produces an open circuit voltage of between 1.4V and 1.8V and has adischarge capacity of between 10 uA-hours and 200 uA-hours. In anembodiment, microbattery 2102 has a total cavity volume of less than 1cubic millimeters. In an embodiment, microbattery 2102 is less than 200μm thick. In an embodiment, microbattery 2102 powers silicon die 206and/or silicon die 306. In an embodiment, microbattery 2102 powers oneor more silicon dies that are substantially similar to silicon die 206or silicon die 306.

FIG. 22 depicts the steps of a flowchart for a process of formingcathode side 1102 of microbattery 2102.

The first step in this exemplary process flow is to etch cavity 203 intotop polymer flex substrate 201 (step 2202) to accommodate a constructionof a cathode of microbattery 2102 (e.g., by laser processing). Theprocess of etching cavity 203 uses a first mask in the process.Subsequent to etching cavity 203, adhesive metal layer 801 (e.g.,titanium tungsten) is deposited into cavity 203 (step 2203) andtransparent conducting oxide 802 (e.g., indium tin oxide) is depositedon adhesive metal layer 801 in cavity 203 (step 2204). Subsequent todepositing transparent conducting oxide 802, photoresist 901 isdeposited over transparent conducting oxide 802 and is photopatternedusing a second mask in the process (step 2208). Areas of unmaskedtransparent conducting oxide 802 and adhesive metal layer 801 aresubtractively etched to create interconnect wiring trace 210 and 214(step 2210). In a subtractive etching process, unmasked areas of amaterial are removed.

Subsequent to creating cavity 1002, the photoresist pattern created instep 2208 is stripped (step 2212) and, using a third mask in theprocess, polymer bondable seal material 1001 (polymer bondable sealmaterial 202 and 213) is applied and photopatterned (step 2214) creatingcavity 1002. Cathode material 1101 is inserted into cavity 1002 (step2216) to complete the construction of the cathode side of microbattery2102 (step 2216).

FIG. 23 depicts the steps of a flowchart for a process of forming anodeside 1902 of microbattery 2102.

The first step in this exemplary process flow is to etch cavity 303,using a first mask in the process, into bottom polymer flex substrate301 (step 2302) to accommodate a construction of an anode ofmicrobattery 2102 (e.g., by laser processing). Adhesion metal layer 1301(e.g., titanium tungsten) is deposited in cavity 303 (step 2304) andseed metal 1302 (e.g., copper) is deposited on adhesion metal layer 1301in cavity 303 to create cavity 1303 (step 2306). Subsequent todepositing seed metal 1302 in cavity 303, deposit photoresist 1401 overseed metal 1302 to completely fill cavity 1303 and form photoresist 1401over bottom polymer flex substrate 301. Using a second mask in theprocess, photopattern photoresist 1401 to create cavity 1502 to exposesurface of seed metal 1302, the anode current collector (step 2308). Thesurface of seed metal 1302 is electroplated with a homogeneous solid toform anode material 1601 (step 2310). In an embodiment anode material1601 is zinc. In another embodiment anode material 1601 is a homogeneoussolid metallic alloy comprising 100 ppm to 1000 ppm Bi and 100 ppm to1000 ppm In, and a remainder is Zn. The remainder of photoresist 1401 isstripped (step 2312).

Photoresist 1701 is deposited over seed metal 1302 and anode material1601 to form a layer of photoresist 1701 over anode material 1601 andseed metal 1302. A patterning of photoresist 1701 defines wiring trace310 and wiring trace 314 and a pattern of seed metal 1302 and adhesionmetal layer 1301 (step 2314). In a subtractive etching process, unmaskedareas of seed metal 1302 and adhesion metal layer 1301 are removed (step2316). In other embodiments, a plurality of wiring traces are defined tomeet a requirement of microsystem 600. The remainder of photoresist 1701is stripped (step 2318). Using a forth mask in the process, polymerbondable seal material 1801 (polymer bondable seal material 302 and 313)is applied and photopatterned to create cavity 1802 (step 2320).Electrolyte separator material 1901 is deposited into cavity 1802forming anode side 1902 of the microbattery, completing the constructionof anode side 1902 of microbattery 2102 (step 2320).

FIG. 24 depicts the steps of a flowchart for a process of formingmicrosystem 600 that includes microbattery 2102.

The first step in this exemplary process flow is to mask and etch cavity203 and cavity 303 into top polymer flex substrate 201 and bottompolymer flex substrate 301 respectively, to accommodate a constructionof a cathode in cavity 203 and an anode in cavity 303 (step 2402). In anembodiment, cavity 212 and cavity 312 accommodate protuberances from theanode side and the anode side of microsystem 600 and are also etched instep 2402. In other embodiments, one or more other cavities are createdon the cathode and/or anode sides of microsystem 600 to accommodatenecessary system components. In an embodiment, the mask used in step2402 is the first mask used in the exemplary process to form microsystem600.

On the cathode side, an adhesion metal layer 801 and a layer oftransparent conducting oxide 802 are deposited in cavity 203 (step2404). On the anode side, adhesion metal layer 1301 and a layer of seedmetal 1302 are deposited in cavity 303 (step 2404).

The anode side is masked and photopatterned to create cavity 1502 andexpose a surface of seed metal 1302 in preparation for electroplatingthe surface (step 2406). In an embodiment, the mask used in step 2406 isthe second mask used in the exemplary process to form microsystem 600.The exposed surface of seed metal 1302 is electroplated with ahomogeneous solid composed of indium, bismuth, and zinc (In/Bi/Zn) toform anode material 1601 (step 2408).

A seed etch mask is applied to the anode side (photoresist 1701) and thecathode side (photoresist 901) and a subtractive etch is performed tocreate interconnect wiring traces 310 and 314 on the anode side andinterconnect wiring traces 210 and 214 on the cathode side (step 2410).In other embodiments, one or more other appropriate wiring traces arecreated to distribute signals and power on microsystem 600. In anembodiment, the mask used in step 2410 is the third mask used in theexemplary process to form microsystem 600.

In an embodiment, the seed etch mask applied in step 2410 is strippedfrom the anode side and the cathode side, exposing the electroplatedanode (anode material 1601) on the anode side and transparent conductingoxide 802 on a floor of 1002 on the cathode side (step 2412). In anembodiment, transparent conducting oxide 802 is indium tin oxide (ITO).

Polymer bondable seal material is applied and photopatterned, creatingpolymer bondable seal material 202 and 213 on the cathode side andcreating polymer bondable seal material 302 and 313 on the anode side(step 2414). In an embodiment, the mask used in step 2414 is the fourthmask used in the exemplary process to form microsystem 600. Cathodematerial 1101 is applied to and fills cavity 1002 on the cathode sideand electrolyte separator material 1901 is deposited into cavity 1802 onthe anode side (step 2416). In an embodiment, cathode material 1101 ismanganese dioxide (MnO2), however, those skilled in the art understandthat other suitable materials can be used.

The anode side and the cathode side are conjoined (step 2418). A firsthandler is removed (temporary support wafer 103), and the outlines ofmicrosystem 600 is laser cut, and then a second handler (temporarysupport wafer 104) is removed (step 2420), creating “C” shapedmicrosystem 500. Those skilled in the art know that the order in whichtemporary support wafer 103 and temporary support wafer 104 are removedis immaterial to the present invention. An opening in “C” shapedmicrosystem 500 is closed by a bonding of rabbet joint adhesive 308 onmicrosystem bottom component 105 with rabbet joint adhesive 208 onmicrosystem top component 106 (step 2422). In an embodiment, afabrication process of microsystem 600 completes in step 2422.

The embodiments of the invention described herein employphotolithographic fabrication techniques, but those skilled in the artknow that other fabrication techniques can be used to fabricatemicrosystem 600, such as electron beam lithography, scanning probelithography, and particle lithography among other techniques.

What is claimed is:
 1. A method for forming a battery, the method comprising: fabricating a cathode in a first cavity in a first dielectric element; fabricating an anode in a second cavity in a second dielectric element, wherein the anode comprises an electroplated homogeneous solid metallic alloy comprising 100 ppm to 1000 ppm Bi, 100 ppm to 1000 ppm In, and a remainder Zn; and joining the cathode and the anode in a complanate manner.
 2. The method of claim 1, wherein the fabricating of the cathode comprises the use of no more than two lithographic masks.
 3. The method of claim 1, wherein the fabricating of the anode comprises the use of no more than three lithographic masks.
 4. The method of claim 1, wherein the fabricating of the anode comprises the use of electroplating.
 5. The method of claim 1, wherein the fabricating of the anode comprises depositing an electrolyte separator material into the second cavity.
 6. The method of claim 1, wherein the fabricating of the anode in the second cavity in the second dielectric element comprises: electroplating the homogeneous solid metallic alloy on a seed metal that is present in the second cavity in the second dielectric element.
 7. The method of claim 6, wherein the electroplating comprises the use of a pulsed current.
 8. The method of claim 1, wherein a concentration of In is in a range of 100 ppm to 500 ppm and a concentration of Bi is in a range of 100 ppm to 500 ppm.
 9. The method of claim 1, wherein the homogeneous solid metallic alloy has a resistivity in a range of about 5×10⁻⁸ to 6×10⁻⁸ ohm-m.
 10. The method of claim 1, wherein the anode has a thickness from 1 micron to 50 microns.
 11. The method of claim 1, wherein the cathode comprises one or more of NiOOH and MnO₂.
 12. The method of claim 1, wherein the fabricating of the anode comprises: electroplating, in any order, a layer of Bi, a layer of In, and a layer of Zn on a surface of a seed layer; and annealing the layer of Bi, the layer of In, and the layer of Zn to provide the homogeneous solid metallic alloy.
 13. The method of claim 1, wherein the fabricating of the cathode comprises: etching the first cavity in the first dielectric element; depositing an adhesion metal layer in the first cavity; depositing a layer of transparent conductive oxide on the adhesion metal layer; depositing a patterned photoresist on the layer of transparent conductive oxide and a topmost surface of the first dielectric element; patterning the layer of transparent conductive oxide and the layer of transparent conductive oxide using the patterned photoresist as a mask; stripping the patterned photoresist; and inserting a cathode material in the first cavity.
 14. The method of claim 13, wherein the transparent conducting oxide comprises indium tin oxide (ITO), indium zinc oxide (IZO), Al-doped zinc oxide (AZO), Ga-doped zinc oxide (GZO) or mixtures thereof.
 15. The method of claim 1, wherein the fabricating of the cathode comprises: etching the second cavity in the second dielectric element; depositing an adhesion metal layer in the second cavity; depositing a layer of seed metal on the adhesion metal layer; and electroplating the homogeneous solid metallic alloy on the layer of seed metal.
 16. The method of claim 1, wherein the fabricating of the cathode comprises: etching the second cavity in the second dielectric element; depositing an adhesion metal layer in the second cavity; depositing a layer of seed metal the adhesion metal layer; electroplating, in any order, a layer of Bi, a layer of In, and a layer of Zn on a surface of a seed layer; and annealing the layer of Bi, the layer of In, and the layer of Zn to provide the homogeneous solid metallic alloy.
 17. The method of claim 1, further comprising cutting the co-joined cathode and anode.
 18. The method of claim 1, wherein the joining of the cathode and the anode comprises a bonding process.
 19. The method of claim 1, wherein the homogeneous solid metallic alloy has a percentage of a volume of voids that is less than 0.01%.
 20. The method of claim 1, wherein the homogeneous solid metallic alloy has no porosity. 